fill nan with other column pandas code example

Example 1: pandas fill na with value from another column

df['Cat1'].fillna(df['Cat2'])

Example 2: pandas replace null values with values from another column

#Python
#Col 1 = where you want the values replaced
#Col 2 = where you want to take the values from
df.["Col 1"].fillna(df.["Col 2"], inplace=True)